This invention relates to the simplification, size reduction and cost reduction of Inertial Measurement Units (IMUs)
Inertial Measurement Units (IMUs) measure the motion of a body in six degrees of freedom using a set of gyroscopes and accelerometers. A typical IMU comprises three gyroscopes and three accelerometers, each a single degree of freedom instrument. They are aligned with respect to three orthogonal axes. They are assembled onto a common member that is sometimes referred to as a xe2x80x9cstable memberxe2x80x9d because it retains the relative alignment and positions of the instruments and, in gimballed guidance and navigation systems applications, it is held aligned to an inertial reference. Typically the instruments are self contained units with their own packages and electronics. And, usually they are representative of different designs, fabrication technologies and materials. IMUs are complex, large and expensive.
This invention relates to the simplification, size reduction and cost reduction of IMUs through MEMS integration. MEMS (Microelectromechanical Systems) is the technology for fabrication and the basis for planar design and design methodologies. MEMS enables the batch fabrication of devices in large quantities to reduce cost. As the technology matures, MEMS will also enable the fabrication of devices having predictable functionality and uniformity. Perhaps not as well appreciated is that MEMS integrates parts into a completed entity. Further assembly and alignment is not required. The advantage of integration is that the uncertainty that normally accompanies the design and fabrication and assembly of separate parts based on dimensioning and tolerancing is reduced.
This invention relates to the exploitation of MEMS integration to design IMUs that take full advantage of integration and to fabricate the full IMU on a common substrate, a chip.
This invention relates to planar gyroscope and accelerometer designs that can be arranged on a chip to sense all degrees of freedom necessary for an application that can be fabricated by the same process.
This invention relates to instrument designs based on a common structure to simplify design and fabrication.
This invention relates to instrument designs that share a common, mechanical structure to provide the same function for each instrument. The increased level of integration reduces the number of parts in the IMU. The common function is a mechanical oscillation.
This invention relates to IMU designs for which one common, mechanical structure provides the same function (mechanical oscillation) for all the instruments. This represents a limit to the reduction in number of overall parts in the IMU and enables the smallest attainable size.
The common mechanical structure becomes the common substrate for all the instruments and can be related to the xe2x80x9cstable memberxe2x80x9d of traditional IMUs, although it is driven in mechanical oscillation.
The main advantage of full integration is the elimination of uncertainty that accompanies the assembly and alignment of separate instruments onto a common member.
A second advantage is the reduction in electronics required to drive each instrument since one set of drive electronics will suffice.
Other advantages include the use of common instrument designs, of a common process being applied to all at the same time, construction based on common materials and a single package. These factors should contribute to a high degree of correlation between the instruments that can be exploited to improve IMU performance.
Generally an Inertial Measurement Unit (IMU) can contain any number of gyroscopes and accelerometers. The typical IMU is a six degree-of-freedom (DOF) design containing three single DOF gyroscopes and three single DOF accelerometers. However some applications do not require the measurement of six degrees of freedom and therefore a lower number of instruments will suffice. It is also true in the case of the six DOF IMU, that more than three gyroscopes and three accelerometers can be used. That is because integration allows the configuration of more sophisticated designs whereby additional instruments are added to build-in redundancy or to operate sets of instruments differentially (with pairs of instruments) to remove common mode errors, etc. Various combinations of gyroscopes and accelerometers will occur to those skilled in the art of IMU design.
Several Considerations apply that drive the MEMS-Integrated IMU design:
Consideration 1 xe2x80x94MEMS integration is a means to achieve optimum performance in a miniature IMU.
Consideration 2xe2x80x94MEMS gyroscopes and accelerometers based on a common structure reduce the requirements on fabrication processes thereby improving yield without which an Integrated IMU is not possible.
Consideration 3xe2x80x94MEMS gyroscopes and accelerometers based on the common structure simplify the IMU design.
Consideration 4xe2x80x94Standard gyroscope and accelerometer designs form the basis for designing various IMUs.
Consideration 5xe2x80x94An integrated IMU makes the most efficient use of space resulting in the smallest size.
Consideration 6xe2x80x94An integrated IMU requires one package that provides a common environment for all instruments.